1. Field of Invention
This invention relates to an active matrix display device.
2. Description of Related Art
The deterioration of liquid crystal is prevented by the common AC driving that gives AC potential to a common electrode and a supplemental capacitance. Low energy consumption is achieved by lowering both electric current and voltage of a drain driver through the minimization of the potential difference between the positive and negative polarities of the video signal inputted to the drain driver in the active matrix display device, in which a video signal is supplied to an independent pixel electrode through a switching element such as a thin film transistor (TFT).
However, the load and the energy consumption of the capacitance in the common electrode and all the supplemental capacitance lines are still large because the voltage polarity of the common electrode and the supplemental capacitance lines are inverted at each horizontal period with the horizontal inversion common AC driving that inverts the polarity of the video signal given to the drain line at each horizontal period.
Japanese Patent Application Publication No. Hei 12-81606 discloses a driving method that can significantly lower the energy consumption by stabilizing the common electrode voltage and by inverting the polarity of the supplemental capacitance voltage and that can simultaneously lower both electric current and voltage of the drain driver through minimization of the potential difference between the positive and negative polarities of the video signal (referred to as “SC driving”, hereinafter).
Also, Japanese Patent Application Publication No. 2003-150127 discloses the dot inversion driving system, in which the voltage with opposite polarity is applied to the pixels in such way that any pair of the adjacent pixels have opposite polarity from each other by supplying the voltage with opposite polarity to the pixel electrodes next to each other in gate line direction, as shown in FIG. 11. The dot inversion driving system can prevent capacitance coupling and the irregularity of the image due to the capacitance coupling that takes place in the SC driving.
However, the dielectric constant of liquid crystal changes according to the change in an applied voltage in the SC driving and the dot inversion driving. Therefore, the potential of the pixel electrode depends on the liquid crystal capacitance and changes non-linearly against the inputted video signal. The potential of the pixel electrode adequate for the inputted video signal voltage cannot be obtained, leading to the deterioration of the gradation characteristics.